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/* crypto/rsa/rsa_oaep.c */
/*
* Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied.
*/
/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
/*
* See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
* http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
* proof for the original OAEP scheme, which EME-OAEP is based on. A new
* proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
* "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
* http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
* for the underlying permutation: "partial-one-wayness" instead of
* one-wayness. For the RSA function, this is an equivalent notion.
*/
#include "constant_time_locl.h"
#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
# include <stdio.h>
# include "cryptlib.h"
# include <openssl/bn.h>
# include <openssl/rsa.h>
# include <openssl/evp.h>
# include <openssl/rand.h>
# include <openssl/sha.h>
static int MGF1(unsigned char *mask, long len,
const unsigned char *seed, long seedlen);
int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
const unsigned char *from, int flen,
const unsigned char *param, int plen)
{
int i, emlen = tlen - 1;
unsigned char *db, *seed;
unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
return 0;
}
if (emlen < 2 * SHA_DIGEST_LENGTH + 1) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
return 0;
}
to[0] = 0;
seed = to + 1;
db = to + SHA_DIGEST_LENGTH + 1;
if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
return 0;
memset(db + SHA_DIGEST_LENGTH, 0,
emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int)flen);
if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
return 0;
# ifdef PKCS_TESTVECT
memcpy(seed,
"\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
20);
# endif
dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
if (dbmask == NULL) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
return 0;
}
if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0)
return 0;
for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
db[i] ^= dbmask[i];
if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0)
return 0;
for (i = 0; i < SHA_DIGEST_LENGTH; i++)
seed[i] ^= seedmask[i];
OPENSSL_free(dbmask);
return 1;
}
int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
const unsigned char *from, int flen, int num,
const unsigned char *param, int plen)
{
int i, dblen, mlen = -1, one_index = 0, msg_index;
unsigned int good, found_one_byte;
const unsigned char *maskedseed, *maskeddb;
/*
* |em| is the encoded message, zero-padded to exactly |num| bytes: em =
* Y || maskedSeed || maskedDB
*/
unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
phash[EVP_MAX_MD_SIZE];
if (tlen <= 0 || flen <= 0)
return -1;
/*
* |num| is the length of the modulus; |flen| is the length of the
* encoded message. Therefore, for any |from| that was obtained by
* decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
* num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus
* irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2.
* This does not leak any side-channel information.
*/
if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2)
goto decoding_err;
dblen = num - SHA_DIGEST_LENGTH - 1;
db = OPENSSL_malloc(dblen);
em = OPENSSL_malloc(num);
if (db == NULL || em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
goto cleanup;
}
/*
* Always do this zero-padding copy (even when num == flen) to avoid
* leaking that information. The copy still leaks some side-channel
* information, but it's impossible to have a fixed memory access
* pattern since we can't read out of the bounds of |from|.
*
* TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
*/
memset(em, 0, num);
memcpy(em + num - flen, from, flen);
/*
* The first byte must be zero, however we must not leak if this is
* true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
* Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
*/
good = constant_time_is_zero(em[0]);
maskedseed = em + 1;
maskeddb = em + 1 + SHA_DIGEST_LENGTH;
if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
goto cleanup;
for (i = 0; i < SHA_DIGEST_LENGTH; i++)
seed[i] ^= maskedseed[i];
if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
goto cleanup;
for (i = 0; i < dblen; i++)
db[i] ^= maskeddb[i];
if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
goto cleanup;
good &=
constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH));
found_one_byte = 0;
for (i = SHA_DIGEST_LENGTH; i < dblen; i++) {
/*
* Padding consists of a number of 0-bytes, followed by a 1.
*/
unsigned int equals1 = constant_time_eq(db[i], 1);
unsigned int equals0 = constant_time_is_zero(db[i]);
one_index = constant_time_select_int(~found_one_byte & equals1,
i, one_index);
found_one_byte |= equals1;
good &= (found_one_byte | equals0);
}
good &= found_one_byte;
/*
* At this point |good| is zero unless the plaintext was valid,
* so plaintext-awareness ensures timing side-channels are no longer a
* concern.
*/
if (!good)
goto decoding_err;
msg_index = one_index + 1;
mlen = dblen - msg_index;
if (tlen < mlen) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
mlen = -1;
} else {
memcpy(to, db + msg_index, mlen);
goto cleanup;
}
decoding_err:
/*
* To avoid chosen ciphertext attacks, the error message should not
* reveal which kind of decoding error happened.
*/
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
cleanup:
if (db != NULL)
OPENSSL_free(db);
if (em != NULL)
OPENSSL_free(em);
return mlen;
}
int PKCS1_MGF1(unsigned char *mask, long len,
const unsigned char *seed, long seedlen, const EVP_MD *dgst)
{
long i, outlen = 0;
unsigned char cnt[4];
EVP_MD_CTX c;
unsigned char md[EVP_MAX_MD_SIZE];
int mdlen;
int rv = -1;
EVP_MD_CTX_init(&c);
mdlen = EVP_MD_size(dgst);
if (mdlen < 0)
goto err;
for (i = 0; outlen < len; i++) {
cnt[0] = (unsigned char)((i >> 24) & 255);
cnt[1] = (unsigned char)((i >> 16) & 255);
cnt[2] = (unsigned char)((i >> 8)) & 255;
cnt[3] = (unsigned char)(i & 255);
if (!EVP_DigestInit_ex(&c, dgst, NULL)
|| !EVP_DigestUpdate(&c, seed, seedlen)
|| !EVP_DigestUpdate(&c, cnt, 4))
goto err;
if (outlen + mdlen <= len) {
if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
goto err;
outlen += mdlen;
} else {
if (!EVP_DigestFinal_ex(&c, md, NULL))
goto err;
memcpy(mask + outlen, md, len - outlen);
outlen = len;
}
}
rv = 0;
err:
EVP_MD_CTX_cleanup(&c);
return rv;
}
static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
long seedlen)
{
return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
}
#endif
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